Hypolipidemic effects of beta-cyclodextrin in the hamster and in the genetically hypercholesterolemic Rico rat

Fermentable carbohydrates exert a more potent cholesterol-lowering effect than cholestyramine

The purpose of this work was to assess the respective role of bile acid excretion and of the end-products of cecal fermentations in the cholesterol-lowering effect of complex carbohydrates. The effects of two different fermentable carbohydrates (guar gum, beta-cyclodextrin), and sequestrant resin (cholestyramine) have been investigated in male Wistar rats. Guar gum and beta-cyclodextrin are broken down in the large bowel, with fermentation rich in propionic acid (37% against 26% for control), whereas cholestyramine did not enhance cecal fermentation. beta-Cyclodextrin and guar gum were less potent than cholestyramine to enhance bile acids and sterol excretion. Nevertheless, fermentable carbohydrates exerted a more potent cholesterol-lowering effect than cholestyramine. beta-Cyclodextrin also depressed triacylglycerol-rich lipoprotein (TGRLP). Fermentable carbohydrates lowered cholesterol of LDL and HDL1 fractions. The induction of hepatic HMG-CoA reductase was practically proportional to rate of fecal steroid excretion. Moreover, with beta-cyclodextrin, hepatic HMG-CoA reductase induction was concomitant to a decrease in fatty acid synthase (FAS) activity. Thus, the cholesterol-lowering effect of fermentable carbohydrates could be related to a depressed lipogenesis, as well as to an accelerated removal of HDL1, in relation to an elevated hepatic demand of cholesterol. In conclusion, fermentable carbohydrates could favour cholesterol elimination and have a general lipid-lowering effect by exerting more complex physiological effects than cholestyramine.

Cellular cholesterol efflux mediated by cyclodextrins

In this study, we compared cholesterol efflux mediated by either high density lipoproteins (HDL3) or beta-cyclodextrins, cyclic oligosaccharides that are able to dissolve lipids in their hydrophobic core. beta-Cyclodextrin, 2-hydroxypropyl-beta-cyclodextrin, and methyl-beta-cyclodextrin at 10 mM induced the release of 50-90% of L-cell [3H]cholesterol after 8 h of incubation, with a major portion of this cholesterol being released in the first 1-2 h of incubation. The cholesterol efflux kinetics are different if cells are incubated with HDL3, which induces a relatively constant rate of release of cholesterol throughout an 8-h incubation. Cholesterol efflux to cyclodextrins was much greater than phospholipid release. To test the hypothesis that maximal efflux rate constants for a particular cell are independent of the type of acceptor, we estimated the maximal rate constants for efflux (Vmax) of cellular cholesterol from L-cells, Fu5AH cells, and GM3468A fibroblasts. The rate constant for HDL3-mediated efflux varied among cell lines in the order Fu5AH > L-cells > fibroblasts. However, these differences were not evident when cyclodextrins were used as cholesterol acceptors. The estimated Vmax values for cyclodextrin-mediated efflux were 3.5-70-fold greater than for HDL3 for the three cell lines. The very high efficiency of cyclodextrins in stimulating cell cholesterol efflux suggests that these compounds can be used in two general ways for studies of atherosclerosis: 1) as research tools to probe mechanisms of cholesterol transport and aspects of membrane structure or 2) as potential pharmacological agents that could modify in vivo cholesterol metabolism and influence the development of the atherosclerotic plaque.

The reproductive and developmental toxicity profile of beta-cyclodextrin in rodents

A 3-generation study with two mating phases per generation and a teratology phase was performed in the rat to assess the reproductive and developmental toxicity of beta-cyclodextrin (beta-CD) in the diet. Transient neonatal growth retardation occurred with 5% beta-CD: a similar, but equivocal, effect was also observed with 2.5%. No permanent defects or other indications of developmental toxicity were found. There was no significant maternal toxicity. The dietary level of 1.25% was found to be a NOAEL for developmental toxicity. Further investigations showed the growth retardation to be specific to dietary administration during lactation: it was not produced by parenteral (i.p.) administration and was not influenced by treatment of the dams or litters during gestation. Slight maternal nutritional deficiency, caused by physico-chemical interactions of beta-CD with nutrients in the gut is proposed as the mechanism of action. No difference in milk composition was found.

Effect of cyclodextrin on plasma lipids and cholesterol metabolism in the rat

beta-Cyclodextrin (beta-CD) is a bile acid and sterol sequestrant produced by enzymatic modification of starch; this product has the potential to decrease plasma cholesterol. In contrast to the sequestrants having resin- or saponin-like properties, beta-CD is rapidly broken down by the large intestine microflora. beta-CD effects on cecal fermentations and lipid metabolism were thus investigated in rats adapted to semipurified diets containing 0%, 2.5%, or 5% beta-CD. In rats fed beta-CD diets, there was an enlargement of the cecum together with a dramatic increase in the cecal concentration of propionic acid (even with the 2.5% level, in moderately acidic pH conditions). Propionic acid produced in the cecum was readily absorbed and entirely taken up by the liver, whereas there was no significant acetic acid uptake. Dietary beta-CD was highly effective in enhancing bile acid entry into to the cecum: the cecal bile acids pool was 2.2 and 3.6-fold enlarged in rats fed the 2.5% and 5% beta-CD diets, respectively. The solubility percentage of bile acids decreased to approximately 25% in rats fed the beta-CD diets (v 51% in controls); the cecal concentration of soluble bile acids was thus relatively low in these animals. The fecal excretion of steroids was strongly enhanced by beta-CD, and bile acids excretion was practically proportional to the dietary beta-CD level. There was a net lipid-lowering effect of beta-CD, even at the 2.5% level. The effect was more pronounced on triglycerides than on cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for the absence of participation of the microbial flora in the hypocholesterolemic effect of guar gum in gnotobiotic rats

Germ-free (GF) and heteroxenic (Hx) rats were given a hypocholesterolemic diet (Hyper) with or without 5% guar gum (GG) for 4 weeks. The GF and Hx rats fed GG diets showed a lower hepatic and plasmatic cholesterol level when compared with Hyper groups. This reduction of cholesterolemia was due to a decrease in the chylomicron + very low density lipoprotein (VLDL) fraction. The caecal and portal concentrations of propionate were 30% higher in Hx rats fed the GG diet than in Hx rats fed the Hyper diet. These results exclude the participation of the intestinal microflora in the hypocholesterolemic effect of GG, and show that guar gum nullifies the effect of the hypocholesterolemic diet in the GF rats.

Interaction of beta-cyclodextrin with bile acids and their competition with vitamins A and D3 as determined by 1H-NMR spectrometry

The interaction of beta-cyclodextrin (beta-CD) with four bile acids, cholic, taurocholic, chenodeoxycholic and lithocholic, was demonstrated by proton-NMR spectroscopy. Lithocholic and chenodeoxycholic acids exhibit a stronger affinity for beta-CD than cholic and taurocholic acids. The affinity of bile acids for beta-CD increases in relation to their hydrophobicity. The competition between these bile acids and the lipophilic vitamins A and D3 in the formation of beta-CD inclusion complexes was studied. These vitamins compete with cholic and taurocholic acids whereas they do not with lithocholic and chenodeoxycholic acids. In the latter case all of the beta-CD present was consumed by the bile acids with the vitamins remaining free in the medium. The affinity of vitamins A and D3 for beta-CD is lower than that of the bile acids. Therefore, when lithocholic or chenodeoxycholic acids are present, the formation of beta-CD inclusion complexes with the vitamins does not occur. The results of this study suggest that depletion of lipophilic vitamins will not occur upon ingestion of beta-CD, thus providing further support for the safety and suitability of beta-CD as an ingredient in foods and orally administered drugs.

Effect of cyclodextrins and undigested starch on the loss of chenodeoxycholate in the faeces

Starch that escapes digestion in the small intestine increases the elimination of chenodeoxycholate and its metabolites in the faeces of both mice and hamsters. In contrast, the elimination of cholate and its metabolites is not increased. In vitro, the affinity of starch for chenodeoxycholate is about 90-fold greater than for cholate. beta-Cyclodextrin, which approximates to one turn of the helical structures formed by the 1,4-linked glucose units of starch, shares these properties. It is proposed that these helical structures in starch act as binding sites for bile salts.